1. Field of the Invention
The present invention relates to a memory device having isolation trenches with different depths and the method for making the same, and more particularly to a memory device that has isolation trenches formed in the peripheral circuit region that are deeper than those in the memory array area.
2. Description of Related Arts
In the present memory manufacturing processes, a shallow trench isolation technique has been widely applied. As an example, the flash memory mainly comprises two areas, a memory array area and a peripheral circuit region, wherein the former is for forming of memory cells, and the latter is for layout design of control circuits.
In the data accessing process of the flash memory, because the low operating voltage is unable to be applied for access of the flash memory, the operating voltage must be maintained at a high voltage level. Therefore, isolation trenches formed in the peripheral circuit region of the memory must have deeper depths to provide a superior isolation effect among the control circuits and to mitigate the problem of leaking current caused from the high operating voltage.
However, in the present memory fabricating process, the memory array area and the peripheral circuit region both utilize the same photo-mask to simultaneously define and form isolation trenches therein, whereby the isolation trenches in the two areas accordingly have the same depth. For the control circuits in the peripheral circuit region, the depth of the isolation trenches is unable to meet the isolation requirement and the leaking current caused by the high operating voltage still exist.
To overcome the mentioned shortcomings, a memory device having isolation trenches with different depths and the method for making the same in accordance with the present invention obviates or mitigates the aforementioned problems.